Dual Binding to Orthosteric and Allosteric Sites Enhances the Anticancer Activity of a TRAP1-Targeting Drug

The molecular chaperone TRAP1 is the mitochondrial paralog of Hsp90
and is overexpressed in many cancer cells. The orthosteric ATP-binding
site of TRAP1 has been considered the primary inhibitor binding location,
but TRAP1 allosteric modulators have not yet been investigated. Here,
we generated and characterized the Hsp90 inhibitor PU-H71, conjugated
to the mitochondrial delivery vehicle triphenylphosphonium (TPP) with
a C10 carbon spacer, named SMTIN-C10, to enable dual binding
to orthosteric and allosteric sites. In addition to tight binding
with the ATP-binding site through the PU-H71 moiety, SMTIN-C10 interacts
with the E115 residue in the N-terminal domain through the TPP moiety
and subsequently induces structural transition of TRAP1 to a tightly
packed closed form. The data indicate the existence of a druggable
allosteric site neighboring the orthosteric ATP pocket that can be
exploited to develop potent TRAP1 modulators.